Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowance for doubtful accounts receivable	$ 3,222	$ 3,404
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, Authorized shares	800,000,000	800,000,000
Common stock, Issued shares	324,418,632	324,418,632
Treasury stock, shares	109,212,809	109,930,832